1. Field of the Invention
The invention relates to a conveyor device for conveying flat articles, in which device the flat articles are moved in series while being at a pitch one from the next that is normally constant, and in which device a synchronization system is provided for compensating for variation in said pitch.
The invention relates more particularly to such a conveyor device that is interposed between a mailpiece unstacker and a bin carrousel directing the mailpieces to sorting outlets.
2. Discussion of the Background Art
European Patent No. 1 214 263 discloses such a belt conveyor device equipped with a synchronization device having elastically deformable wheels driven in rotation at variable speed. That conveyor is designed to move mailpieces ranging from an ordinary letter of thickness less than 1 millimeter (mm) to a mailpiece or “flat” of large format and of thickness as large as 32 mm.
The bins of the carrousel move above the sorting outlets at a constant speed. Each bin is loaded with a mailpiece coming from the conveyor.
The unstacker is controlled by a periodic reference signal having its frequency aligned on the frequency with which the bins go past the free end of the conveyor.
When a mailpiece is unstacked in response to an edge of the reference signal being detected, it passes firstly through the synchronization device in which it undergoes an acceleration/deceleration stage so as to be brought to the speed of the belts of the conveyor. It is then taken in charge by the belts of the conveyor so as to be brought at constant speed to the bin carrousel. The instant at which the mailpiece is input into the synchronization device is detected on the basis of a passage sensor that makes it possible to adjust an acceleration profile for the mailpiece within the synchronization device in such a manner as to make the arrival of the mailpiece at the end of the conveyor coincide with the instant at which an empty bin serving to receive the mailpiece goes past.
At the end of the conveyor, the instant at which the mailpiece arrives is monitored so as to check that it is neither too early nor too late relative to the expected coincide time, and if it is, the mailpiece is directed to a reject outlet before being reinserted into the inlet of the unstacker. In practice, in that known device, the period with which the bins go past the conveyor is 333 milliseconds (ms). The time window for presenting a mailpiece to an empty bin, on either side of the coincide time extends from −15 ms late to +20 ms early. Outside that time window, the mailpiece is not injected into a bin, but rather it is deflected to the reject outlet.
It has been observed that, with a highly mixed batch of mailpieces, i.e. a batch covering a broad spectrum of mailpieces ranging from letters to large-format flat articles or “flats”, it is possible to have a high percentage of mailpieces rejected, which can affect the throughput of the machine.
Documents EP 1 683 586 and EP 0 818 406 disclose synchronizer devices in which mailpiece speed is adapted as a function of detecting mailpiece thickness or weight, so as to obtain inter-mailpiece pitch that is constant.